So if you're familiar with late-3.5 edition content, from the mechanical side the Murī should look very familiar - they're heavily based on the Karsites from Tome of Magic. However, for obvious reasons we can't use them: to start, there was no Karsus on Finiens for them to be descended from, and for another we wanted a localized backstory for them.
Enter Ladybug/Scintillae, one of the core worldbuilders in my group and the developer of the country of Divus. While their primary residents, the Ael-Varan (who I'll be going into detail on shortly) were my creation, it's Lady who developed almost the entirety of their culture, history, and background, basing them heavily on the Roman Empire at its height. One of the regular penchants she put in their history was a habit of unregulated magic and mad science, and the creation of the Murī was but one of many such incidents in their history. I'm very much looking forward to touching on all the countries of the world once I'm done with the races, as some of the historical events we've worked out have developed into some really interesting stories, many of which I'd love to just write up or turn into stories or games or something.
In the original idea for the race, the Murī were all human-descended, and we were planning on working out individual Murī-ized variants of the rest of Finiens's races, or at least the ones native to Wachara where the opportunity of being affected by the Murī alteration was likely. However, some various discussions and in-game conversations on the subject that occurred in the months since their idea was finalized, and the decision was eventually made to have it be a template that could be freely applied instead.
Between the Arachnes and the Murī, though, this is probably as good a place as any to note the use of Level Adjustment in some of our races. Both of these races are level-adjusted to one level behind the norm, as are the Tuatha if someone should choose to play one; they use a modified version of Pathfinder's Noble Drow statistics, with the type changed to Fey and a few alterations to their spell-like abilities. I know a lot of players are very touchy about Level Adjustment as a feature, especially after it was used (and perhaps overused) in 3.5 for almost anything that wasn't a standard race, regardless of whether or not most of them actually were worth the difference. A fair number of Pathfinder players react very negatively to the merest hint of using Level Adjustment in a PF or PF-based game, but I've never been one of them.
I've actually found LA to be a fairly useful tool, if it's applied reasonably. The only races we use in Finiens that have LA are the ones that are very clearly of superior power level by a large margin, such as the Tuatha and Arachnes, or that are templates that stack with the original racial abilities and increase their power significantly, such as the Murī. Everything else - from the core six races (recall that there are no Half-Orcs in Finiens) to the various Pathfinder races we use to our other homebrewed creations - has no adjustment and levels up as normal. It's really just a lot simpler that way.
We're really just getting started with this latest batch of races, making our way across the continent of Wachara westward and detailing the rather large array of races native there as we go. Coming up next we'll have the transformative Entomorphs, the elite Girtablilu, the persistent Fenrin, the imperial Ael-Varan, the elegant Thriae, the enigmatic Leanaí-Dubh, the curious Civil Harpies, the industrious Warforged, and the anarchic Ti'Larinn.